Relationship between physiological excitatory and inhibitory measures of excitability in the left vs. right human motor cortex and peripheral electrodermal activity.

The current study was aimed at investigating the relationships of excitatory and inhibitory circuits of the left vs. right primary motor cortex with peripheral electrodermal activity (EDA). Ten healthy subjects participated in two experimental sessions. In each session, EDA was recorded for 10 min from the palmar surface of the left hand. Immediately after EDA recording, Transcranial Magnetic Stimulation (TMS) was used to probe excitatory and inhibitory circuits of the left or right primary motor cortex using two protocols of stimulation: the input-output curve for recording of motor evoked potentials, for testing excitatory circuits; the long-interval cortical inhibition (LICI) protocol, for testing inhibitory circuits. In both cases, motor evoked potentials were recorded with surface electrodes from a contralateral hand muscle.The main results showed that in the right motor cortex, excitatory circuits directly correlate and inhibitory circuits inversely correlate with sympathetic activation. In the left motor cortex, both exci- tatory and inhibitory circuits are inversely correlated with sympathetic activation. These findings may suggest a bi-hemispheric mode of control of vegetative system by motor cortices, with the right hemi- sphere mainly involved in sympathetic control.